DIY Audio Projects Forum

Hi Rogers

Thanx

It's great that you're open and understanding, for mods of your construction !

Tom and I are talking about ( in PM's ) making a hybrid power amp, but more about that, in a new threat later.

Regards form Kramme

Hi guys!

I'm finally rolling on this project after getting my Adcom amp running. Per Rogers suggestion, I breadboarded the psu. I used 1n4006 diodes, qty. 2 4700 uF (35V) caps, and qty. 2 resistors (2.2k). My transformer is a 24V ac wall wart (pretty hefty of course).

Looks pretty good from the model but I decided to hook up the tube....and nothing. Not even a faint glow. On the first cap, I was reading about 14 V, but on the second cap, 0 V. I calculated the resistance of the filament (83 ohms) for the 12au7a. I went back and plugged that into the model and got about .1 V. Aha! Apparently, it is no good to have 83 ohms across the last cap. Which was why I got 0 V on my DMM set at 200 V scale.

I've got lots to learn. A breadboard is a really good thing to have in your arsenal!

_________________
Rega P25 and LFD Mistral phono (analog) or Oppo DVD Player (digital) > Aunt Corey's Buffered Pre > Adcom GFA 535 > Spica TC-50

The Tangentsoft CMoy tutorial is really good to go through to get some breadboarding ideas.
http://www.tangentsoft.net/audio/cmoy-t ... t-0150.pdf
It may help give you some good layout ideas.

Also, take a look at the Apheared 47 Headphone amp for more ideas: http://benfeist.com/a47/

Cheers, Gio

_________________
[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]

Hi guys, I scanned through the posts (quickly), so apologies if this question was asked before. I have assembled the amp and when testing it, there was no sound, up until I removed the 1uF cap from the circuit. I resoldered it other way round, but still, no sound when it is in the circuit.

If I remove it, I have sound!!! But, the lower end sounds distorted

What could cause this??

ion,
You have a cross connection somewhere. With the 1uF cap out of circuit there is no path from the first stage to the second stage. One nice thing about the original schematic is there are many connections to ground-- but it can get confusing. Take some pics of top and bottom of your amp.

Rogers

I only have the top view with me, I'll take a shot of the bottom tonight. The green and blue wires coming from the tube to the proto board, is where I removed the cap. That is left and right ch.

I will take a deeper look at the board. Take a snapshot of the bottom of the tube as well. Are you using a 12au7, ecc82 or ecc88?


Rogers

Hi. I'm using a 12AU7 tube. Here is a pic (a bit blurry) of the underside so long. Can't find the pic of the tube. Will take another one if I can't find it.

Has anyone made a PCB for this little amp? Willing to ship/post?

I basically have my little amplifier built now, and actually am listening to it as I am writing this.

It sounds amazing! A bit low on gain strait from the ipod, but I have a simple NPN 3904 solution to get more gain.

But as for the resistor filtured power supply..... I love the sound of it but it requires very high wattage resistors to stay cool, and I do not have a 22 ohm 10 watt resistor on hand, and the filturing is insane!!!!

And the first swithcing supply was noisy and I could not keep the amp cool in it's puny case.... It also got some kind of shorting bug that I could not understand when I was going to use it on my 25EH5 amp (still not tested after rebuild) My friend plugged the supply in one day and it literally blew up! and burned!!!!! notsure why but I pulled it out and my friend destroyed what was left of the power supply with a crow-bar

I am now using my amp with an old millitary 12 volt supply that actually sounds nearly as good but in a way better than the resistor/wallwart supply.... but it is massive and too old to find parts to make a modern one.

So it is just one problem after another, but it is all because of finding the right power supply! I need one that is most likely regulated but does not sacrifice the great sound of a resistor filter supply, but it also has to be of a portable size too.

So, really what are my options Tube regulated low voltage?

_________________
My Mini 12AU7 Tube Preamp, Pioneer SX-D7000, JVC XL-V221BK, JBL L80T, DCM TF700

• Project Page - Mini 12AU7 Tube Preamplifier
• Support/Questions - Mini 12AU7 Tube Preamp thread